Performance of graphite/LiFePO_4 battery after high temperature storage

The performance of graphite/lithium iron phosphate(LiFePO4) battery after stored at high temperature(55±2 ℃) was studied.During stored in 25%～75% state of charge(SOC),the capacity of both the battery and the LiFePO4 electrodes slightly increased firstly and then decreased.When the capacity went up to the maximum,the impedance of the LiFePO4 electrode decreased with its kinetic characteristics improved,mainly contribute to the overall changing of performance.The reason was the difference in the cell volume of LiFePO4 and FePO4 caused the internal stress in the structure when stored in delithiated,which led to the partical splitting of the two phases,some fresh surface emerged.